Owing to their lightweights, easy processability, impact resistance, etc., the plastic products are used in various applications including containers, automobile instrument panels and outer plates, window materials, roof materials, wrapping materials, various housing materials, optical disc substrates, plastic lenses, base materials in display devices such as liquid crystal displays, plasma displays, projection TVs, etc.
Among them, for examples, resin materials such as polycarbonates, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, styrene-based resins including acrylonitrile-butadiene-styrene copolymer (ABS), methyl methacrylate-styrene copolymer (MS resin), acrylonitrile styrene copolymer (AS resin) etc., vinyl chloride-based resins, cellulose acetate including triacetyl cellulose are suitable for the above applications, because they are excellent particularly in lightweights, easy processability, impact resistances, etc.
However, these plastic products are easily damaged due to low surface hardness. Transparent resins such as a polycarbonate and polyethylene terephthalate have a defect that their inherent transparency or appearance is conspicuously damaged. Thus, this makes it difficult for the plastic products to be used in fields requiring abrasion resistance.
Under the circumstances, active energy ray-curable hard coat materials (coating materials) giving abrasion resistance to the surfaces of the plastic products have been sought. However, since cured layers of commercially available, active energy ray-curable hard coat materials are largely shrunk to cause warping, peeling off or cracking, it is difficult to coat them thick. Consequently, there was a limit on the attainable hardness and scratching resistance.
In order to solve such problems, various active energy ray-curable coating materials have been recently proposed, which would realize hardness and abrasion resistance that exceed those in the conventional methods. For example, JP-A 11-309814 discloses that abrasion resistance is largely improved by coating two or more layers of coating agents, while using an inorganic coating agent having a coated film formability, such as polysilaxane, for the outermost layer. However, since the coating agent is inorganic, it is difficult to form a thick film. Thus, since it is substantially necessary to apply two or more layers, there is a problem of poor processability.
On the other hand, a trial is made, in which hardness and abrasion resistance are improved by coating two or more layers of coating agents having different coefficients of elasticity. For example, JP-A 2000-52472 describes that a coated film having high hardness is obtained by making the coefficient of elasticity of a first layer of a coating agent larger than that of a second layer of another coating agent. U.S. Pat. No. 6,489,015 (JP-A 2000-214791) also describes that a coated film having hardness is obtained by setting the coefficient of elasticity of a first layer coating agent larger than that of a second layer of another coating agent. However, in any of them, the total thickness of the coated film becomes at least 10 μm, and processability is poor in that two or more layers are applied.
Furthermore, U.S. Pat. No. 6,846,567 (JP-A 2000-219845) describes that excellent abrasion resistance can be realized, while the total thickness of coated films is set to at most 10 μm, when a methacrylic polymer is applied as a first layer, and on the first layer, as a second layer, a coated film, which is obtained by curing an organosiloxane resin comprising a hydrolysis condensate of colloidal silica and a specific silicate, is laminated. However, there is no change the application of two or more layers.
Meanwhile, coating agents capable of realizing excellent hardness and abrasion resistance even if applied in a single layer have been investigated. Heretofore, compositions of colloidal silica and multifunctional acrylates, hydrolysis condensate compositions of colloidal silica and a specific silicate, and curable resin compositions of the above and a polyfunctional acrylate, an epoxy resin, a phenoxy resin or the like, or compositions of the above compositions and an acryl resin, etc. have been widely investigated as organic-inorganic composite coating agents. However, they had problems of insufficient-hardness and abrasion resistance, poor stability in the form of a coating liquid, or insufficient environmental properties (moisture resistance, heat resistance, etc.) of cured films, etc. As compared with them, an active energy ray-curable coating agent including a compound obtained by reacting a polyfunctional acrylate with a colloidal silica as disclosed in U.S. Pat. No. 5,378,735 (JP-A 5-287215) and U.S. Pat. No. 6,160,067 (JP-A 9-100111) has more excellent hardness and abrasion resistance, even if coated in a single layer, than the conventional organic-inorganic composite coating agents. However, since they had low antifouling property and weatherability, and further sufficient surface curing cannot be realized when they are applied in the form of a thin film, it was difficult to realize the physical properties that should essentially appear.
Further, for example, as shown in JP-A 10-316864, a method for using a polymerized UV curable resin is proposed to decrease shrinkage. However, although shrinkage is largely reduced on curing, it has a limit in the case that it is adopted in applications requiring further reduction in shrinkage or applications requiring higher hardness and scratching resistance, in addition, the resin is susceptible to interruption on curing with oxygen, and particularly has a problem in curing a thin film (for example, film thickness: at most 2 μm). Furthermore, since a cured degree in a surface portion is low even in the case that the film is not thin, there are many problems in the durability of the physical properties.
Moreover, in order to further lower the shrinkage or improve the cured degree of the surface, there are proposed a method using a cationic polymerizable resin as a (polymerized) UV curable resin (JP-A 2001-40205, etc.), and a method using a colloidal silica to which a cationic polymerizable low molecular-weight organic component is suggested (JP-A 2002-53659, etc.), and a method using these components and an ordinary radical polymerizable UV curable resin (including both organic and organic-inorganic hybrid resins) in combination (For example, JP-A 9-278935, JP-A 2002-128887, JP-A 2002-322430, U.S. Pat. No. 6,777,102 (JP-A 2003-147017, etc.). Although they have the characteristics of reduced shrinkage, increased film thickness or enhanced surface curing, there is still a limit in application to usages requiring further increased hardness and scratching resistance. Further, there are still many problems in affording antifouling property and weatherability.
Meanwhile, there are many examples regarding antifouling coating agents (For example, coating films obtained from a specific fluorine-containing polymer or a silicone-containing polymer (JP-A 61-275365, JP-A 10-279834, JP-A 2002-37827, JP-A 2002-241146, JP-A 2003-165928, JP-A 2003-313385, etc.). However, they had a problem in durability of the performance, particularly the durability of the antifouling property, especially when the scratching resistance was poor.
As a method for solving such problems, the present inventors have investigated various active energy ray-curable compositions each containing a copolymer, as an essential component, which copolymer contains acryl groups and polysiloxane groups in side chains and further contains fluorine-containing alkyl groups if needed (For example, JP-A 2000-80169, JP-A 2001-98188, JP-A 2002-194084, etc.). Further, JP-A 2003-335984 describes that an active energy ray-curable resin composition containing a copolymer which has fluorine or a polysiloxane and also contains acryl groups forms a cured film having an excellent balance among the antifouling property, high hardness and scratching resistance.
Although coated films obtained from these compositions had relatively good antifouling property and durability, the level required for the antifouling property has recently become high, and it has come to be not said that the performance is sufficient particularly in applications of recently developed next-generation type optical discs in which writing and erasing are performed with blue laser, touch panel displays for car navigators, PDA and cellular phones, large flat panel displays for liquid crystal TVs and plasma TVs, etc. This is because such antifouling copolymers themselves have relatively low hardness and their curing property is not high.
Since the composition was often applied in a thin film particularly in the case of such applications, there were many problems particularly in the durability the physical properties and the antifouling properties in such cases.
Further, in the case of the optical recording media such as optical discs, etc. and optical articles such as touch panels, etc. contamination with a stain of a fingerprint or a contaminant such as dust influences not only the appearance but also the performance. This results in increased writing/reading disorder, errors at the time of writing/reading, etc. particularly in the case of the optical recording media.
Recently, as the high density optical recording media, an optical disc is proposed in which the writing/reading beam size is decreased and the recording density per unit density is increased to a few times or more of that of the DVD through shortening the writing/reading wavelength to around 400 nm or increasing the numerical aperture (N/A) of an objective lens. For example, they are BLU-RAY DISC™ (high-density optical disc) and HD DVD.
As the writing/reading beam size decreases, the diameter of the beam on a surface at a beam-incident side also decreases. Therefore, the disc is sensitive to a stain on the surface of the medium, so that writing/reading disorders or errors are likely to occur. Further, a stain containing an organic substance like a fingerprint causes a problem that once it attaches, it is difficult to be removed.
As methods to solve such problems, for example, JP-A 10-110118 proposes that a non-crosslinking type fluorine-based surface active agent is added into a coated film of a hard coat on a surface of a disc substrate, and JP-A 11-293159 proposes that crosslinking type and non-crossing type fluorine-based surface active agents are simultaneously added thereinto. However, further improvement of the performance is needed.
US-A1 2004-013976 (JP-A 2002-245672) and JP-A 2002-234906 describe that an optical disc on which is formed a hard coat film composed of an organic-inorganic hybrid resin composition that contains a slipping agent of such as an acryl resin or modified silicone with an organopolysiloxane group have an excellent slipping property. However, they are mainly aimed at protecting a media placed in cartridges, but pay no attention to the stains of the fingerprints. Further, the slipping property and the fingerprint resistance (so-called antifouling property) are fundamentally different, and most of the slipping agents generally have insufficient fingerprint resistance (so-called antifouling property).
US-A1 2005-191410 (JP-A 2004-152418) and US-A1 2005-072336 (JP-A 2005-112900) describe that an optical recording medium having a layer of a specific hard coat which contains a silicone-based compound or a fluorine-based compound with active energy ray-curable groups exhibits excellent fingerprint resistance. However, although an attaching area of a fingerprint can be reduced because of excellent water-repellent and oil-repellent properties, it could not be said that a fingerprint wiping-off property and its durability are sufficient.